Study On Two Kinds Of Mafic Ultramafic Rocks And Nickel Sulfide Deposit In East Kunlun Island Arc Zone

Eastern Kunlun Orogenic Belt experienced a complex and lengthy history of tectonic evolution and mineralization,riching in mineral resources and Mafic-ultramafic intrusions.In recent years,the discovery of several copper nickel sulfide deposits in this belt,such as Xiarihamu,Binggounan and Shitoukengde,show that the eastern Kunlun tectonic belt has the conditions and potential for magmatic nickel copper sulfide deposit.two typical mafic-ultramafic intrusions,Xiarihamu and Dagele,are selected to study in this paper.Through the study of geology,chronology,petrology,mineralogy,mineralogy and geochemistry,the tectonic environment of the copper nickel sulfide deposit in the eastern Kunlun tectonic zone are revealed and the oretical basis for regional prospecting are provided.The main results of this study are summarized as follows:?1?The surrounding rocks of the two kind of mafic-ultramafic rock are the Paleoproterozoic Jinshuikou group.Ore-bearing mafic-ultramafic rock intrusive contact with surrounding rocks,another mafic-ultramafic rock are the constituent part of the ophiolites,and tectonic contact with surrounding rocks.?2?The Xiarihamu intrusion,outcropped about 1.33km²,is a ferruginous basic-ultrabasic intrusion with ratio of m/f ranging from 2.48 to 6.30.The copper-nickel ore and mineralization are mainly produced in No.I and No.?intrusions,which are typical layered complex with clear cumulate layering.Rock types are abundant and mainly composed of peridotite facies,pyroxenite facies and nortic-gabbro facies rock.Rock structures show that the fractional crystallization plays a leading role in the magma evolution,and the main cumulate phases are olivine and orthopyroxene.?3?The morphology of ore body mainly are stratoid and lenticular,.Its occurrence is basically consistent with the rock mass and had a trend of plunging towards southwest in deep.The main ore structures are massive,sideronitic and disseminated.According to the ore structure and interspersing relationship,the metallogenic process can be divided into in-situ segregation,ore pulp injection and hydrothermal mineralization.?4?Xiarihamu No.?,No.?and Dagele magnesium peridotite rocks are part of Ophiolite.The ophiolite is composed of serpentine,gabbro,eclogite and garnet amphibolite.The eclogite undergone two stages of metamorphism:eclogite-facies metamorphism and amphibolite-facies retrograde metamorphism.The former mineral assemblage are garnet+omyroxene+rutile,the latter are hornblende+diopside+plagioclase.The composition of garnet is Alm51⁶3,Gross 19³4,Pyrope 7²4,belongs to the C type eclogite,which is formed by high pressure metamorphism during deep subduction.JD component of omyroxene is 28³7.?5?The results of zircon LA-MC-ICP-MS U-Pb dating of No.I intrusion show that the crystallization ages of gabbronorite is 439.1±3Ma,suggesting Xiarihamu intrusions formation in the Silurian.?6?Xiarihamu rocks have clear cumulate structure and higher values of?³⁴S?+4.44‰⁺6.45‰?compared to the mantle source and xenoliths of surrounding rock show that fractional crystallization and assimilation are the main mechanisms of sulfide segregation.In addition,sulfur from crust source is the main source of metallogenic material.?7?The geochemical characteristics show that Xiarihamu and Dagele ophiolites have been affected by subduction fluid and had IAT characteristics.All indicated that ophiolite belong to SSZ type related to the island arc environment,the protolith of the eclogite is basalt in the ophiolite suite,amphibolite fades retrogressive metamorphism took place during the later exhumation process.?8?All rocks of Xiarihamu Nickel deposit,ophiolite and Dagele ophiolite show LREE enriched appreciably pattern,enriched in LILE and depleted in Ta,Nb,Ti,which indicates island arc information.The composition of Sr-Nd isotopic in No.I intrusion all in the range of enrichment mantle type and the primary magma belongs to high magnesium tholeiite magma containing 10.7%MgO.The mantle source should be the mantle wedge above the subducting slabs.?9?The two types of rocks are located in the north of the middle East Kunlun fault,and controlled by Heishan-Nalinggele fault.The output of the eclogite and ophiolite shows that it is a lithospheric fracture and the middle East Kunlun belt is an important suture zone.?10?The metallogenetic process of the Xiarihamu nickel deposit can be divided into:Magma formed by partial melting of the mantle wedge intrudes along the fracture,and then differentiation in the deep magma chamber,a part of the mafic magma moves away from,the residual magma enters terminal magma chamber and the fractional crystallization and separation of sulfide occurs.The ore pulp then penetrated,and hydrothermal further activates ore-forming materials.?11?Combined with the geochronology,geochemical and structural background,it is considered that Xiarihamu deposit is formed in the tensive island arc,which is beneficial to the formation of nickel deposits.The Paleozoic is another main metallogenic period of nickel deposit.